This specifies the factorization should be done over the rationals extended by

:
Here the factorization is done over the rationals extended by

and
I:
By default,
PolynomialGCD treats algebraic numbers as independent variables:
This computes the GCD over the algebraic number field generated by the coefficients:
By default,
Together treats algebraic numbers as independent variables:
With
Extension->Automatic,
Together recognizes algebraically dependent coefficients:
By default, the norm is computed in the field generated by the
AlgebraicNumber object:
This computes the norm in the field in which the
AlgebraicNumber object is represented:
This computes the norm in the field generated by

: